1. Field of the Invention
The present invention relates to an actuator, and more particularly to an actuator with self-locking assist device.
2. Description of the Prior Art
Actuator is usually used in various kinds of equipments (such as ventilator, automatic door, cupboard, satellite antenna hoisting device, elevating wheelchair, height-adjustable hospital bed, drawing table, massage chair, transportation equipment, height-adjustable computer desk or rehabilitation equipment) to achieve automatic operation.
As shown in FIG. 1, an actuator 10 comprises a first pipe 11 and a second pipe 12 inserted in the first pipe 11. In the first pipe 11 is axially pivoted a screw 13 on which is axially mounted a gear 131. Through the gear 131 the screw 13 is connected to and rotated by a power source. The second pipe 12 has one end positioned at one end of a nut 132 and is to be pushed to move back and forth along the first pipe 11.
After further analyzing the above structure, we found it still has the following problems: once the actuator 10 is used for carrying load, after the screw 13 stops rotating, the self-locking of the actuator 10 depends on the friction among relative components. Hence, the phenomenon that the weight of the load makes the actuator move due to the incapability of self-locking is likely to occur, making the second pipe 12 which previously extended out move back into the first pipe 11 again, and as a result, the actuator 10 will move uncontrollably because of the influence of the load carried, and thus the safe use of the actuator cannot be ensured.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.